聚晶金刚石复合片(PDC)应力表征方法的探讨

聚晶金刚石复合片是采用HPHT方法生产的,所以不可避免地在界面处、以及聚晶金刚石层内部的缺陷处存在大量的残余应力。本文主要围绕聚晶金刚石复合片的应力表征问题进行了实验和理论分析。实验、研究表明,聚晶金刚石复合片在聚晶金刚石层内存在着宏观应力和微观应力,即第一类内应力、第二类内应力;聚晶金刚石表面应力的大小可以反映聚晶金刚石层的应力存在状况;XRD方法可以用于聚晶金刚石复合片应力的表征。     

XRD方法在聚晶金刚石复合片界面应力表征中应用的研究

借助XRD方法对不同生产工艺、无齿、有齿型硬质合金基底制备的PDC制品进行了研究。表明：聚晶金刚石复合片在聚晶金刚石层内存在着宏观应力和微观应力；聚晶金刚石复合片表面应力大小可以反映聚晶金刚石层的应力存在状况；聚晶金刚石复合片残余应力的大小与XRD图谱的斜率成正比，因此XRD方法可以用于聚晶金刚石复合片应力的表征。     

PDC性能优化及其钎焊技术研究现状

聚晶金刚石复合片（PDC）因其优良的性质，广泛应用于机械加工、能源开采、地质勘探等方面。但是PDC温度敏感性较高，在高温下内部残余应力增大、金刚石层发生氧化、石墨化等现象，导致PDC金刚石骨架撕裂、金刚石颗粒剥落、甚至复合片失效。从PDC表面改性、粘结剂优化、PDC结构设计、晶粒细化以及PDC钎焊技术等五个方面综述了PDC国内外研究现状，讨论了PDC存在的共性问题，并对未来的研究方向进行了展望。     

粗颗粒聚晶金刚石复合片显微结构的分析

利用扫描电镜、光学影像仪等分析检测仪器,在不损伤被检样品的物理性能、状态和内部结构的条件下,从聚晶金刚石层与基体的界面结构,微观的均匀性以及金刚石层D—D键的结合情况等方面定性判断PDC性能的优劣。研究发现：金刚石和硬质合金界面结构为非平面连接时,其性能优于传统的平面结合型;PDC材料聚晶金刚石层中金刚石在空间相连形成D-D结合立体网络状结构,这是PDC材料力学性能优异的主要原因,且D—D键越多,复合片性能越好。     

聚晶金刚石复合体的主要性能研究状况

主要从衡量聚晶金刚石复合体PDC质量好坏的三大指标--耐磨性、耐热性、抗冲击韧性着手,在国内外学者对PDC性能较完整的测试和研究结果的基础上,综述了聚晶金刚石复合体的性能及其影响因素,着重对PDC表面石墨化、氧化现象、粘接剂的选择、界面形态的改进、粒度范围、组装程序、烧结工艺等作了概述,概括了几种典型聚晶金刚石复合体机械性能,为金刚石复合片的合成工艺及其工业应用提供一些参考.     

聚晶金刚石复合片的磨损规律

通过观察切削花岗岩过程中聚晶金刚石复合片(PDC)刀具的磨损过程和磨损形貌,研究PDC刀具的磨损规律。研究结果表明:切削花岗岩时,受切削力及其冲击的作用,PDC刀具产生近乎平行岩石表面的磨损形式,磨损机理为机械作用引起聚晶金刚石层微观裂纹产生并扩展而导致的金刚石颗粒的微观破碎。     

金刚石复合片的界面形态及性能特点

聚晶金刚石复合片的失效主要发生在金刚石与基体之间的界面处,改变界面的化学组分和形状可以改善复合片的使用性能。本文介绍了几种优质复合片的界面形态及其性能特点。在金刚石层与基体之间添加镀碳的钨片,或在金刚石层外镀上几层金属,可以改善金刚石与基体的不匹配问题;在基体上加工出沟槽或锯齿,使复合片抗冲击性能显著提高;为了避免直线型沟槽的方向性以及降低在尖端出现的应力集中,将沟槽或锯齿做成环形并使其尖角改成光滑的圆角;降低锯齿尖端粘结剂的含量,可使基体与金刚石的膨胀系数和弹性模量更接近而提高热稳定性;把界面做成波浪形,并且使界面与复合片的轴线不垂直,以此来分散应力。     

聚晶金刚石复合片无损检测方法的探讨

本文在分析聚晶金刚石复合片（PDC）无损检测技术（NDT）的基础上,针对POC复合片的主要缺陷,探讨了利用便携式超声波探伤仪对PDC进行无损检测的可能性。得出了实验条件下PDC分层、裂纹缺陷的超声波测试波形图和主要技术参数如下。工作方式：单探头（单一发射,强度不变）;检波方式：双波;频段：中等;声压：2dB。扫描量程：10mm;脉冲移动位置：8．82mm。实验结果表明：本方法对PDC的分层、裂纹等缺陷有明显的特征反应。     

影响聚晶金刚石复合片性能的因素及改进方法

聚晶金刚石复合片作为PDC钻头的切削元件，其质量的好坏直接影响着整个钻头的钻进速率及使用寿命。影响复合片质量和性能的主要因素是金刚石与粘接剂的配比、粘接剂的种类、金刚石的粒度、金刚石／硬质合金界面结构以及烧结工艺等。本文探讨了不同种类粘接剂的优、缺点；介绍了如何通过改变金刚石颗粒的粒度分布提高复合片的耐磨性和抗冲击性能；在金刚石，硬质合金界面处添加碳化物形成元素薄片以及采用金属镀层(如W等)实现界面的冶金结合，从而提高界面的结合强度；采用锯齿形界面并伴随成分梯度过渡、以及采用正弦曲线形界面结构可明显改善复合片的性能。这些方法可为工业上生产优质复合片提供参考。     

钻探用聚晶金刚石复合片的显微组织及性能

采用上层为细粒度金刚石、下层与硬质合金接触的为粗细度金刚石的分层设计理念，制备钻探用多金刚石层的聚晶金刚石复合片（PDC），对比不同粒度的单层金刚石PDC与多层金刚石PDC的显微组织与性能的差异。利用超声波扫描、扫描电子显微镜（SEM）表征每种PDC的内部缺陷和表面形貌等，并分别对PDC的耐热性、抗冲击性和耐磨性进行测试。结果表明：多层金刚石PDC的综合性能良好，其表层耐磨，下层更耐冲击，且其具有更加均衡的耐热性、抗冲击性和耐磨性。细粒度金刚石层PDC的耐磨性更高，但耐热性和抗冲击性较低，而粗粒度金刚石层PDC的耐热性和抗冲击性能更好，但耐磨性较差。     

Research on polycrystalline diamond compact (PDC) with low residual stress prepared using nickel-based additive

Polycrystalline diamond compact (PDC) with low residual stress was synthesized using nickel-based additive (Ni₇₀Mn₂₅Co₅) as sintering solvent at high temperature/pressure (HTHP). A systematic study of the residual stress in a polycrystalline diamond (PCD) layer was performed using micro-Raman spectroscopy. The stress was measured by determining the Raman shift and was approximated as being biaxial to calculate the magnitudes of stress. Sintering process parameters such as temperature, the diamond size and content of binder additive were all found to affect residual stress levels. The sample with low stress measured on the surface of PCD is compressive and has an average value of 0.10 GPa. Scanning electron microscopy (SEM) analysis of morphology shows that the dense microstructure with diamond-diamond (D-D) direct bonding has formed in the PCD layer. X-ray diffraction (XRD) performed in the cross-section of PCD confirmed the presence of diamond, nickel-based alloy, WC and Co_xW_xC.     

Effect of cobalt content on the performance of polycrystalline diamond compacts

Cobalt was an indispensable role in the damage of a PDC cutter due to its inevitable adverse thermal effect like thermal catalysis, thermal expansion and thermal oxidation in the welding and drilling process, while the quantitative studies on its serial thermal damage effect were still seldom reported. In order to understand the damage mechanism of a PDC cutter and therefore design better products, it was quite necessary to study the roles of cobalt in the PDC cutter by a quantitative means. In present study, the total cobalt content of the PCD layer of polycrystalline diamond compacts were adjusted by blending different amount of microsized cobalt powder in the mixed diamond grains and the infiltrated cobalt from the cemented carbide cylinder during the HTHP sintering process. The sintered PDC cutters were examined by XRD, SEM, EDX, vertical lathe tests, and impact tests, and it was found that the abrasive ratios of the fabricated PDC cutters were strongly dependent on the cobalt content of sintered diamond layers. The PDC cutter without adding cobalt powder exhibited the best resistance to the abrasion, while the PDC cutters sintered by adding 4% mass of cobalt powder demonstrated the worst abrasive ratio, which was the direct proof confirming that by decreasing the content of residual cobalt in the PCD layer the resistance of the PDC cutter to the abrasion would be improved significantly. A non-destructive characterization method was adopted based on the statistical calculation was proposed by using Matlab and Image-J software to quantitatively explore the relationship between the cobalt content as well as the average size of residual cobalt in the PCD layer and the abrasion performance, which opened a new technical route for the disclosure of cobalt-dependent abrasion resistance for the PDC cutter analysis. Moreover, a cobalt-rich narrow zone was found to appear in the interface of PCD/cemented carbide, which was deduced to be the main reason to cause the delamination of PCD layer from the cemented carbide. It was also interesting to find that the percentage of added cobalt powders seemed no adverse effect on the impact performance of the PDC cutters. The conclusion of present study about the cobalt role in the PDC performance was quite good for understanding the PDC damage modes and helped for the better design and fabrication of PDC.     

Thermal residual stress of polycrystalline diamond compacts

Thermal residual stresses in polycrystalline diamond compact(PDC)cutter arising from the difference in thermal expansion between the polycrystalline diamond(PCD)and the supporting tungsten carbide substrate after sintering at high pressure and high temperature were investigated using finite element simulation,laboratory tests and theoretical analysis.The obtained results show that although compressive residual stresses exist both in the interface of PCD table and in the most region of PCD table surface, the...     

界面结构对PDC抗冲击性能的影响

本文采用重陀倾斜式方法测试了不同界面结构的PDC的抗冲击韧性,并对PDC冲击破坏机理进行了讨论,对界面结构以及其它因素对PDC抗冲击性能的影响进行了探讨和研究.结果表明:重陀倾斜式方法能够较好地反应PDC钻头工作时的实际受力情况;在同一工艺参数下,PDC层与硬质合金基体之间的界面结构对PDC的抗冲击性能影响很大;随着界...     

Micro-Raman and X-ray diffraction stress analysis of residual stresses in fatigue loaded leached polycrystalline diamond discs

Polycrystalline diamond (PCD) cylindrical tool-bits used in oil well drilling are susceptible to fracture due to the hostile environment of randomly occurring high impact loads. These tool-bits generally comprise of a PCD layer sintered onto a Co-cemented tungsten carbide substrate. The cobalt metallic phase primarily aids the formation of the diamond to diamond bonds, however during application the same cobalt expands much quicker than the diamond, breaking the very same bonds it helped to form in the first place, leading to premature failure of the tool bits. As the PCD is virtually a two-phase material comprised of cobalt and diamond, substantial volumes of the metallic phase can be removed through a leaching process without compromising the cohesiveness of the diamond matrix, with reported improved wear resistance and thermal stability. X-ray diffraction and Raman spectroscopy techniques were used to investigate residual stresses in leached polycrystalline diamond disc samples. A systematic investigation and evaluation of the average in-plane residual stress fields using the Raman technique showed a progressive shift of the residual stress state from a compressive stress state to an average tensile stress state as a function of increasing number of loading cycles. In contrast the X-ray diffraction method recorded compressive stresses for all the measurements even at the highest number of loading cycles. The apparent disagreement between the two sets of results were satisfactorily explained by considering the probing beam size and sampling depth for the two different but complementary techniques.     

聚晶金刚石复合片界面微观结构对性能的影响

以硬质合金基体及优选的主晶为25μm的金刚石颗粒为原料,在2种工艺下用国产铰链式六面顶压机高温高压制备聚晶金刚石复合片(PDC),研究PDC界面处微观结构对其性能的影响。结果表明：工艺1制备的PDC界面处存在类树枝状枝晶金属池,其是硬质合金中的金属元素向聚晶金刚石层方向迁移形成的,主要元素为C、W、Co;而工艺2制备的PDC中不存在此类现象。工艺1制备的PDC的耐热温度为870℃,抗冲击等级为32,磨口面积为5.860 mm²;工艺2制备的PDC的耐热温度为920℃,抗冲击等级为45,磨口面积为5.166 mm²。工艺2制备的PDC相对于工艺1制备的PDC,其耐热温度、抗冲击性能和耐磨性能分别提高50℃、40.6%和11.8%。     

?58mm聚晶金刚石复合片的合成及表征

利用国产六面顶压机,合成出了?58 mm的聚晶金刚石复合片。超声波微成像分析表明,样品无分层、裂纹、金刚石层厚度不均等缺陷。导电性及切削测试显示,实验合成的粒度尺寸为25 μm的58GD-025刀片及混合粒度的58GM-253的切割速度与耐磨性均表现优异。